Diverter valve? I can get hot water eventually but I have to jiggle programmer, changed Honeywell control on diverter valve but no different, any ideas?

This boiler, from memory, has an electric diverter valve.
If the system has dirty (sludge/scale laden) water then the diverter valve may not return under spring pressure, and therefore not divert all of the hot boiler water to the hot water heat exchanger, leaving some going to the rads.
If I am right then the rads will not get fully hot.
If the valve has failed completely, or electrically, then the rads will get fully hot and there will be no hot water output (hot water will be cold).

F04 is a fume thermostat fault

If this a honeywell valve you may need to change the motor in side the valve , sounds like its lost some of it power to move the inside of the valve to y postion .

without seeing it its hard to say, the thermostat controls the boiler and/or diverter valve depending how its been wired, the diverter valve shunts the water to were its needed ie from one circuit to another if you have two therostats there is a conflict somewere, best bet to have an engineer sort the wireing out

Yes it could be something other than the motor but I think you are right yo start there.Good luck and thank you

It depends on your system some will only work with hot water on and heating do you have two zone valves?

sounds like your circulating pump is bad or electronic zone valves

Check to see if diverter valve is in domestic mode or heating mode.

with y plan 3 connections on programmer HW on HW off CH on HW on to cylinder stat then HW call to Orange on Mvalve to power boiler and pump HW off to grey wire on Mvalve to close hot water CH to room stat common then heating call to white on Mvalve

have you got a motorised valve problem